The following disclosure relates to a novel polymeric composite including a nanoparticle filler, and a process for making the composite using a masterbatch. More particularly, the disclosure provides a novel method for the production of a nanocomposite including a polymer and a halloysite nanoparticle filler, the filler having the general shape of a cylinder or rolled scroll-like element, in which the diameter of the cylinder is less than about 500 nm. The advantages of the nanoparticle filler (e.g., reinforcement, flame retardant, improved or equivalent mechanical performance) are provided as a result of the ability to disperse the nanoparticle within and/or on the surface of a polymeric structure.
The addition of various nano-clay materials to polymer systems can lead to improved mechanical properties (such as toughness/ductility, fatigue resistance or strength), improved processability and/or thermodynamic stability. Details of such advantages as well as alternative materials and their characteristics are found, for example, in several prior patent applications relating to halloysite nanocomposites and applications thereof, including U.S. patent application Ser. No. 11/469,128 for a “POLYMERIC COMPOSITE INCLUDING NANOPARTICLE FILLER,” by S. Cooper et al., filed Aug. 31, 2006; U.S. application Ser. No. 11/531,459 for “Radiation Absorptive Composite and Methods for Production” filed Sep. 13, 2006 by A. Wagner et al.; and U.S. Provisional Application 60/867,369 for “POLYPROPYLENE NANOCOMPOSITE MASTER BATCH COMPOSITION AND METHOD OF MANUFACTURE,” filed Nov. 27, 2006 by B. Dillon Boscia et al., the disclosures of all of the above-identified applications being hereby incorporated by reference in their entirety.
Composite materials have become well known as man-made materials are increasingly substituted for naturally occurring materials in construction, parts manufacture and the like (e.g., automobiles, building materials, food packaging and textiles). A polymer composite in this context includes at least one polymer matrix or material in combination with at least one particulate filler material. The polymer matrix material may be any of a number of polymers including themoplastics such as polyamide (Nylon), poly-urethane, polyolefins, vinyl polymers, and the like, thermosets, and elastomers. As structure-property relationships of composites become better understood, the use of nanoparticles is of increasing interest in the formation of composites—referred to as nanocomposites. Some of the most common nanoparticle fillers are two-dimensional nanoclays, one-dimensional carbon nanotubes, and zero-dimensional metal oxide nanoparticles such as Zinc Oxide (ZnO), Titanium Dioxide (Ti02), and Zirconia (ZrO). Composites offer the potential of materials having properties that are not often available in naturally occurring materials (e.g., U.S. Pat. No. 6,518,324 to Kresta et al. for a Polymer Foam Containing Nanoclay).
There are several known ways in which to form polymer nanocomposites utilizing nanoclay materials. These processes include melt compounding, precipitation, and utilization of a masterbatch. The following disclosure is directed, in one embodiment, to the use of a masterbatch as the means by which a polymer nanocomposite is produced. A masterbatch includes a high concentration of halloysite nanoparticles (e.g., up to 50% by weight of halloysite nanotubes), and is produced and then subsequently combined with neat polymer, for example in an extrusion or molding process, to form the final nanocomposite.
The advantages of using a concentrated masterbatch in the preparation of final nanocomposite materials, particularly those produced in accordance with the description below, are numerous. One advantage is that the final composite may exhibit better dispersion of the nanoparticles within the final material/product, further resulting in improved mechanical properties because of the more consistent dispersion. Defects in the final composite, due to poor dispersion, would lead to weak points in the final part formed, thus potentially compromising its mechanical properties. The nanotubes are well dispersed when the masterbatch is formed, making dilution to the final use composition for extrusion or molding an easy task. This two step process allows two opportunities to fully separate the tubes for maximum effectiveness. Also, making a concentrate limits the amount of polymer that must go through a separate compounding step and, therefore, reduces the operational cost of using the composite.
In melt compounding processes for nanomaterial fillers there is typically an upper limit to the amount of filler which can be incorporated. There is usually an increase in viscosity at high loading levels, resulting in high shear that will cause the polymer system to degrade to the detriment of the final mechanical properties. This requires high energy utilization and thus high cost, relative to standard polymer composite processing. For platy clays in particular the problem is made worse because the filler must be fully exfoliated during the extrusion process. Exfoliation requires the use of significant amounts of organic treatment agents that interfere with the polymer processing. In addition, to fully exfoliate and disperse a material such as a platy clay, a barrel length-to-diameter (L/D) ratio much greater than 40:1 is required and therefore necessitates specialized extrusion equipment.
For halloysite materials high concentrations of halloysite nanotube filler (e.g., HNT™ from NaturalNano, Inc.) are easily obtained for masterbatches for two reasons. First, the halloysite has already been processed to produce a primary particle that does not need to be exfoliated. Therefore, neither large amounts of organic additives are required nor unusual processing equipment or formulations. Second, the addition of the halloysite nanotubes does not produce significant increases in melt rheology and, in fact, for most polymers reduces the resistance to melt flow—producing a polymer composite formation process that is easier to run than simply melting the polymer itself. Composites made using the halloysite nanotube masterbatches (e.g. HNT™ from NaturalNano, Inc.) provide excellent ductility, elongation and fatigue resistance. By using a masterbatch, the material may also be provided in commercial quantities to facilitate use of the nanoparticle filler, yet avoiding inherent problems with handling clays (e.g., dusting).
Disclosed in embodiments herein is a method of producing a polymer nanocomposite, comprising: surface treating a nanofiller; forming a masterbatch by blending the nanofiller and polymer; forming particles (e.g., precipitate, pellets, flakes, etc.) of the masterbatch; dry blending masterbatch material with neat polymer to form a mixture; melt blending the mixture; and forming a final product using the melt-blended mixture.
Also disclosed in embodiments herein is a polymer nanocomposite masterbatch for letdown with a neat polymer, comprising: from about 5 wt % to about 50 wt % of a nanoparticulate filler (or about 5 wt % to about 60 wt %) and a polymer.
The various embodiments described herein are not intended to limit the invention to those embodiments described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the appended claims.